Quality control is an essential part of high-volume printing processes. Despite ever-increasing reliability of print engines and other web processing devices, it is not uncommon for errors to occur on a section of a long printed web. In production, a continuous web of printable material is processed in a single run and, typically, at a later time the web is separated into sheets for further processing and sorted. In such high volume operations, it is often difficult to identify individual errors on the web.
A typical scan of a web for errors involves either a manual or automated inspection of the web at predetermined intervals. The web is sometimes slowed or stopped to allow visual inspection. Most scanning equipment is incapable of adequately checking the web at high speed and, thus, error checking is usually performed only at intervals.
When an operator or an automated mechanism locates an error at a given interval, a reprint must be performed to replace the damaged web section (typically one or more "pages"). At this time, the operator must decide how many pages to replace. The operator must use a judgment in determining how much of the web requires reprinting. One disadvantage to this technique of error checking is that it requires a decision on the part of the operator as to the number of sheets to replace. In addition, the damaged section must be tracked, thenceforth, as part a larger continuous web, to insure that it is eliminated when the web is rewound onto a receiving roll, or is processed in a post-production operation. In substance, the manual location of erroneous web sections is time-consuming, imprecise and requires substantially tracking technology that increases the risk of unreliable printing.
It is, therefore, an object of this invention to provide a system that detects errors in a web and provides a quick and effective solution for eliminating errors without employing complex tracking techniques. The system should generate minimal waste of usable web sections and should enable accurate reproduction of eliminated web sections so that the total desired volume of the print run is achieved.